Abstract
The aim of this work was to map and identify the Phytophthora sojae Avr1c gene. Progeny from a cross of P. sojae strains ACR10×P7076 were tested for virulence on plants carrying Rps1c. Results indicate that avirulence segregates as a dominant trait. We mapped the Avr1c locus by performing whole genome re-sequencing of composite libraries created from pooled samples. Sequence reads from avirulent (Pool1) and virulent (Pool2) samples were aligned to the reference genome and single nucleotide polymorphisms (SNP) were identified for each pool. High quality SNPs were filtered to select for positions where SNP frequency was close to expected values for each pool. Only three SNP positions fit all requirements, and these occurred in close proximity. Additional DNA markers were developed and scored in the F2 progeny, producing a fine genetic map that places Avr1c within the Avr1a gene cluster. Transient expression of Avr1c or Avr1a triggers cell death on Rps1c plants, but Avr1c does not trigger cell death on Rps1a plants. Sequence comparisons show that the RXLR effector genes Avr1c and Avr1a are closely related paralogs. Gain of virulence on Rps1c in P. sojae strain P7076 is achieved by gene deletion, but in most other strains this is accomplished by gene silencing. This work provides practical tools for crop breeding and diagnostics, as the Rps1c gene is widely deployed in commercial soybean cultivars.
Highlights
Plants are challenged by a diversity of pathogens and rely on pre-existing and elaborated defense mechanisms including innate immunity
The P. sojae strains ACR10 and P7076 differ in virulence towards soybean plants carrying the Rps1c gene; ACR10 is avirulent while P7076 is virulent
The soybean Rps1c gene is extensively deployed for the management of root and stem rot disease caused by P. sojae
Summary
Plants are challenged by a diversity of pathogens and rely on pre-existing and elaborated defense mechanisms including innate immunity. Host plants detect microbe-associated molecular patterns (MAMPs) and pathogen effector molecules by use of immune receptors positioned on the outer plasma membrane or inside the cell cytoplasm [1]. In many cases host immune receptors and pathogen effector proteins underlie resistance (R) and avirulence (Avr) gene interactions described by plant pathologists. P. sojae effectors that are recognized by Rps proteins and cause ETI are Avr factors. Each Avr gene is predicted to encode a small secreted protein containing a signal peptide followed by an RXLR (Arg-any amino acid-Leu-Arg) sequence. This conserved motif is proposed to have a role in the delivery of the effector protein to the host cell cytoplasm [11,12]. Additional conserved features in the C-terminal or effector domains of the proteins are suggested to be important functional elements [13,14]
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